Hydrofluorocarbon (HFC) products are widely utilized in many applications, including refrigeration, air conditioning, foam expansion, and as propellants for aerosol products including medical aerosol devices. Although HFC's have proven to be more climate friendly than the chlorofluorocarbon and hydrochlorofluorocarbon products that they replaced, it has now been discovered that they exhibit an appreciable global warming potential (GWP).
The search for more acceptable alternatives to current fluorocarbon products has led to the emergence of hydrofluoroolefin (HFO) products. Relative to their predecessors, HFOs are expected to exert less impact on the atmosphere in the form their lower GWP. Advantageously, HFO's also exhibit low flammability and low toxicity.
As the environmental, and thus, economic importance of HFO's has developed, so has the demand for precursors utilized in their production. Many desirable HFO compounds, e.g., such as 2,3,3,3-tetrafluoroprop-1-ene or 1,3,3,3-tetrafluoroprop-1-ene, may typically be produced utilizing feedstocks of chlorocarbons, and in particular, highly chlorinated propanes, e.g., tetra- and pentachloropropanes.
Unfortunately, these higher chlorides have proven difficult to manufacture using acceptable process conditions and in commercially acceptable regioselectivities and yields. For example, conventional processes for the production of pentachloropropanes provide unacceptable selectivity to the desired pentachloropropane isomer(s), i.e., 1,1,2,2,3-pentachloropropane, require the use of high intensity process conditions and/or catalyst systems that are difficult to utilize in large scale production processes and/or that are not recoverable once used. Other conventional processes may be limited to the addition of a single chlorine atom per reaction pass, and so must be repeated until the desired number of chlorine atoms has been added, with each additional step requiring additional capital, energy, and other cost investment. Still others require starting materials that are either cost prohibitive, have limited availability or both.
Further, the dehydrochlorination steps required to create alkenes from a feedstream comprising alkanes conventionally are conducted with the use of caustic, resulting in large quantities of waste water including low value by-products such as sodium chloride. Conventional processes rely on many such dehydrochlorination steps, thus multiplying the amount of waste water that must be treated prior to disposal.
It would thus be desirable to provide improved processes for the production of chlorocarbon precursors useful as feedstocks in the synthesis of refrigerants and other commercial products. More particularly, such processes would provide an improvement over the current state of the art if they provided a higher regioselectivity relative to conventional methods, required low intensity process conditions, and/or made use of catalyst systems and/or initiators that are recoverable or otherwise reusable, or were capable of the addition of multiple chlorine atoms per reaction pass as compared to conventional processes. Further advantages would be provided if lower cost and/or more widely available starting materials could be utilized.